Glycol aldehyde is a well known compound and is a useful intermediate for the preparation of other valuable products. For example, ethylene glycol, a valuable end product, as well as an intermediate, can be prepared from glycol aldehyde by hydrogenation. Processes for the production of glycol aldehyde by the reaction of formaldehyde with carbon monoxide and hydrogen in the presence of certain rhodium catalysts are described in the co-pending application of Alwyn Spencer, Ser. No. 256,183, filed Apr. 21, 1981 and the co-pending application of W. Eamon Carroll et al Ser. No. 290,622, filed Aug. 5, 1981, both of which applications are assigned to the same assignee as the present application, and in U.S. Pat. No. 4,200,765, issued to Richard W. Goetz on Apr. 29, 1980. The present invention is an improvement over the processes described in the aforesaid applications, both of which describe the use of formaldehyde or paraformaldehyde as a reactant--in contrast to the use of hemi-formals as reactants in the present invention. By using a hemi-formal instead of formaldenyde or para-formaldehyde, a number of advantages are gained, namely, no water is generated in the reaction system, any formaldehyde which is generated or released in the course of the reaction is readily converted to a hemi-formal and used for further reaction in the process, and there is no significant loss of formaldehyde per se or as hemi-formal in the overall operation of the present process.
As to the aforementioned patent, it is not believed to be any more pertinent to the present invention than the aforesaid applications because the patent makes no mention of the use of hemi-formals in the preparation of glycol aldehyde. The formaldehyde reactants disclosed in the above patent are formaldehyde, paraformaldehyde, methylal (formal) having the formula CH.sub.2 (OCH.sub.3).sub.2 and polyoxymethylene.
As noted above, ethylene glycol can be produced by a two step process in which glycol aldehyde is an intermediate which is then hydrogenated to form the glycol. U.K. Patent Application GB No. 2,070,002A published Sept. 3, 1981, discloses a method for making ethylene glycol in which a formaldehyde di-sec-alkyl acetal is reacted with CO and H.sub.2 using a single component catalyst of cobalt carbonyl to form an ethylene glycol mono-sec alkyl ether which is then hydrolyzed with water using an acidic catalyst to form ethylene glycol. The acetal employed described as having the formula ##STR1## where R.sup.1 and R.sup.2 are each independently an alkyl group such as methyl, ethyl, propyl and butyl groups. Besides using an acetal which is different from hemi-formals employed in the present invention, the above application employs a cobalt-carbonyl catalyst which is quite different from the rhodium catalysts employed in the present invention.